The present invention is concerned with cancer treatment and diagnosis, especially with melanoma associated peptide analogues, epitopes thereof, vaccines against and diagnostics for the detection of melanoma and for the monitoring of vaccination.
During the stepwise changes from normal to tumor tissue, tumor-associated antigens appear. The characteristics of tumor-associated antigens are very much dependent on the origin of the tumor carrying them. The existence of antigens associated with animal tumors was documented in the last century, and the antigenic character of human cancers has been well established, primarily through recent studies with monoclonal antibodies.
Attempts to isolate and chemically characterize these antigens have encountered serious difficulties, many having to do with a lack of reagents suitable for precipitation of the antigen-bearing molecules from a solution.
Like many other stimuli, the tumor-associated antigens activate not one but a whole set of defense mechanisms—both specific and unspecific, humoral and cellular. The dominant role in in vivo resistance to tumor growth is played by T lymphocytes. These cells recognize tumor-associated antigens presented to them by antigen presenting cells (APCs), and will be activated by this recognition, and upon activation and differentiation, attack and kill the tumor cells.
Cytotoxic T lymphocytes (CTL) recognize short peptide fragments of 9-11 amino acids in length, which are presented in the antigen-binding groove of Major Histocompatibility Complex (MHC) class I molecules (Townsend et al., 1986, Cell 44.959; Bjorkman et al., 1987, Nature 329:512). These peptides are usually derived from intracellular protein pools and associate in the lumen of the endoplasmic reticulum with MHC class I heavy chain and β2-microglobulin molecules, followed by transportation of the MHC-peptide complex to the cell surface. Despite the presence of many putative antigenic peptides within the same antigen, only a few peptides are selected for recognition by CTL.
MHC Class I/II antigens are often down regulated in solid tumors. This may affect all class I/II antigens, or only part of them. Viral and cellular peptides that can sensitize appropriate target cells for cytotoxic T lymphocyte mediated lysis may fail to do so when produced in cells with a low level of expression of MHC class I antigen. Cytotoxic sensitivity may be induced, at least in some cases by raising the level of MHC class I/II antigen expression by interferon γ and tumor necrosis factor α.
The MHC class I binding-affinity of an epitope is an important parameter determining the immunogenicity of the peptide-MHC complex. Analysis of Human histocompatibility antigen (HLA-A *0201)-restricted epitopes recognized by anti-viral CTL demonstrated that several peptides bind to HLA-A *0201 with high affinity. Furthermore, immunogenicity analysis of motif containing potential epitopes using HLA-A *0201 transgenic mice revealed that a threshold MHC class I affinity was required for a peptide in order to elicit a CTL response Messing et al., 1995, J. Immunol. 154:5934; Sette et al., 1994, J. Immunol. 153:5586). In addition to the MHC class I-binding affinity, stability of peptide-MHC complexes at the cell surface contributes to the immunogenicity of a CTL epitope. Consequently, MHC class I binding-affinity and stability of peptide-MHC complexes are important criteria in the selection of specific peptide determinants for development of CTL-epitope based therapeutic vaccines.
Recently, a number of antigens have been identified as target antigens for anti-melanoma CTL. Using a genetic approach, the tumor specific antigens MAGE-1 and -3, as well as the melanocyte-lineage specific antigen tyrosinase, were identified (van der Bruggen et al., 1991, Science 254:1643; Gaugler et al., 1994, J. Exp. Med. 179:921; Brichard et al., 1993, J. Exp. Med. 178:489).
In the co-owned and co-pending patent-application (EP 0 668 350), the gp100 melanocyte-specific protein was identified as a target antigen for melanoma tumor infiltrating lymphocytes.
Recently, two other melanocyte differentiation antigens, Melan-A/MART-1 and gp75, were identified as target antigens for anti-melanoma CTL (Coulie et al., 1994, J. Exp. Med. 180:35; Kawakami et al., 1994, Proc. Natl. Acad. Sci. USA. 91:3515; Wang et al., 1995, (vol 181, pg 799, 1995). J. Exp. Med. 181:1261. 10-12). Eight HLA-A *0201 restricted epitopes derived from these antigens have now been characterized, displaying varying affinities for HLA-A *0201 (Wolfel et al., 1994, Eur. J. Immunol. 24:759; Cox et al., 1994, Science 264:716; Kawakami et al. 1995. J. Immunol. 154.3961; Bakker et al., 1995, Int. J. Cancer 62:97; Kawakami et al., 1994, J. Exp. Med. 180:347; Castelli et al., 1995, J. Exp. Med. 181:363).